Add spec for GitLab issue 51

https://gitlab.com/arctic-fox/spectator/-/issues/51

spec/issues/gitlab_issue_51_spec.cr

@@ -0,0 +1,107 @@
+require "../spec_helper"
+
+private class Foo
+  def call(str : String) : String?
+    ""
+  end
+
+  def alt1_call(str : String) : String?
+    nil
+  end
+
+  def alt2_call(str : String) : String?
+    [str, nil].sample
+  end
+end
+
+private class Bar
+  def call(a_foo) : Nil # Must add nil restriction here, otherwise a segfault occurs from returning the result of #alt2_call.
+    a_foo.call("")
+    a_foo.alt1_call("")
+    a_foo.alt2_call("")
+  end
+end
+
+Spectator.describe Bar do
+  mock Foo, call: "", alt1_call: "", alt2_call: ""
+
+  let(:foo) { mock(Foo) }
+  subject(:call) { described_class.new.call(foo) }
+
+  describe "#call" do
+    it "invokes Foo#call" do
+      call
+      expect(foo).to have_received(:call)
+    end
+
+    it "invokes Foo#alt1_call" do
+      call
+      expect(foo).to have_received(:alt1_call)
+    end
+
+    it "invokes Foo#alt2_call" do
+      call
+      expect(foo).to have_received(:alt2_call)
+    end
+
+    describe "with an explicit return of nil" do
+      it "should invoke Foo#call?" do
+        allow(foo).to receive(:call).and_return(nil)
+        call
+        expect(foo).to have_received(:call)
+      end
+
+      it "invokes Foo#alt1_call" do
+        allow(foo).to receive(:alt1_call).and_return(nil)
+        call
+        expect(foo).to have_received(:alt1_call)
+      end
+
+      it "invokes Foo#alt2_call" do
+        allow(foo).to receive(:alt2_call).and_return(nil)
+        call
+        expect(foo).to have_received(:alt2_call)
+      end
+    end
+
+    describe "with returns set in before_each for all calls" do
+      before_each do
+        allow(foo).to receive(:call).and_return(nil)
+        allow(foo).to receive(:alt1_call).and_return(nil)
+        allow(foo).to receive(:alt2_call).and_return(nil)
+      end
+
+      it "should invoke Foo#call?" do
+        call
+        expect(foo).to have_received(:call)
+      end
+
+      it "should invoke Foo#alt1_call?" do
+        call
+        expect(foo).to have_received(:alt1_call)
+      end
+
+      it "should invoke Foo#alt2_call?" do
+        call
+        expect(foo).to have_received(:alt2_call)
+      end
+    end
+
+    describe "with returns set in before_each for alt calls only" do
+      before_each do
+        allow(foo).to receive(:alt1_call).and_return(nil)
+        allow(foo).to receive(:alt2_call).and_return(nil)
+      end
+
+      it "invokes Foo#alt1_call" do
+        call
+        expect(foo).to have_received(:alt1_call)
+      end
+
+      it "invokes Foo#alt2_call" do
+        call
+        expect(foo).to have_received(:alt2_call)
+      end
+    end
+  end
+end